I assume the engine monitor is monitoring engine usage since last oil change. This is part of the oil life monitor (OLM). 50300-42300 = 8000 miles that you have put on the truck since purchase. 400 hours - 170 hours = 230 hours. This is how many hours you have had the engine running since you purchased the truck. 8000 / 230 = ~35 miles per hour. That sounds like a reasonable average speed to me. Seems like it's working just fine.
Unless of course this has nothing to do with the OLM, in which case, it's been reset or something is broken.